Lane-keep assisting system for vehicle

ABSTRACT

A system for assisting a lane-keep traveling of a vehicle is comprised of a camera for detecting a view ahead of the vehicle, a vehicle behavior detector including a vehicle speed sensor and a yaw rate sensor, and a controller. The controller is arranged to estimate a road shape on the basis of lane markers detected by the camera, to detect a target yaw rate necessary to return the vehicle at a center of the lane markers, and to determine that there is a possibility that the vehicle deviates from the lane when a difference between the target yaw rate and an actual yaw rate detected by the yaw rate sensor becomes greater than a threshold.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a system and method forassisting lane-keep traveling of a vehicle, and more particularly to alane-keep assisting system which determines whether a vehicle tends todeviate from a lane according to a vehicle traveling condition on thelane.

[0002] Japanese Patent Provisional Publication No. 11-348697 discloses asystem for assisting a vehicle to travel along a lane. This system isarranged to generate alarm on the basis of a relative position of thevehicle relative to lane markers.

SUMMARY OF THE INVENTION

[0003] However, in the case that the vehicle travels along asmall-radius corner, the alarm is not generated even if the vehicle isnot steered along the corner, and the alarm is generated only when therelative distance between the vehicle and the lane marker becomessmaller than a predetermined value. Further, even when the vehicle isturning a corner along a lane, this known system generates alarmcontinuously or intermittently according to the small relative distance.

[0004] It is therefore an object of the present invention to provide alane-keep assisting system which accurately detects that the vehicletends to deviate from a traveling lane.

[0005] An aspect according to the present invention resides in a systemfor assisting a lane-keep traveling of a vehicle. The system comprises aroad image detector, a vehicle behavior detector and a controller. Theroad image detector takes a view ahead of the vehicle. The vehiclebehavior detector detects a behavior of the vehicle. The controller iscoupled to the road image sensor and the vehicle behavior detector. Thecontroller is arranged to calculate a road shape on the basis of theview taken by the road image detector, to calculate a target turnindicative value indicative of a target turn for reaching the vehicle toa target position, on the basis of the road shape detected, to calculatean actual turn indicative value indicative of an actual turn of thevehicle, and to determine whether the vehicle approaches a lane boundaryof a traveling lane, on the basis of the target turn indicative valueand the actual turn indicative value.

BRIEF DESCRIPTION OF THE DRAWINGS

[0006]FIG. 1 is a schematic view showing a first embodiment of alane-keep assisting system according to the present invention.

[0007]FIG. 2 is an explanatory view showing an installation position ofa camera employed in the system of FIG. 1.

[0008]FIG. 3 is a flowchart showing a lane marker detecting processemployed in the first embodiment.

[0009]FIG. 4 is a view employed for explaining model lane markers.

[0010]FIG. 5 is a view employed for explaining a method for settinginitial values of candidate lane marker search areas.

[0011]FIG. 6 is a view employed for explaining the setting method of theinitial values of the search area under a condition that lane markershave been already detected.

[0012]FIG. 7 is a view employed for explaining the search area settingmethod on a road image.

[0013]FIG. 8 is a view employed for explaining a detecting method ofcandidate lane marker points.

[0014]FIG. 9 is a view showing an offset quantity between a candidatelane marker point just detected and a point on the model lane markerpreviously detected.

[0015]FIG. 10 is a flowchart showing a traveling condition monitoringprocess of the first embodiment.

[0016]FIG. 11 is a view employed for explaining a method for detecting alateral displacement at a fixation point.

[0017]FIG. 12 is a view employed for explaining the operation of thesystem according to the present invention.

[0018]FIG. 13 is a flowchart showing the traveling condition monitoringprocess of a second embodiment.

[0019]FIG. 14 is a control map showing a relationship between a vehiclespeed and a threshold.

[0020]FIG. 15 is a schematic view showing a third embodiment accordingto the present invention.

[0021]FIG. 16 is a flowchart showing the traveling condition monitoringprocess of the third embodiment.

DETAILED DESCRIPTION OF THE INVENTION

[0022] Referring to FIGS. 1 to 12, there is shown a first embodiment ofa lane-keep assisting system S according to the present invention.

[0023] As shown in FIG. 1, the lane-keep assisting system S is installedto a vehicle VE and comprises a CCD camera 1, an image processor 2, acontroller 3, a yaw rate sensor 4, a vehicle speed sensor 5, an alarm 6and an alarm controller 6 a.

[0024] CCD camera 1 is installed in a passenger compartment of vehicleVE. More specifically, camera 1 is installed at an upper and laterallycenter position near a front window as shown in FIG. 2 so that a yawangle θ between an optical axis of a lens of camera 1 and a longitudinalcenter axis of vehicle VE is zero and a pitch angle therebetween is α.Camera 1 takes an image of a road view ahead of vehicle VE. Imageprocessor 2 is coupled to camera 1 and receives data of the image takenby camera 1. Image processor 2 processes the image in order to detectlane markers of a traveling lane and sends the processed image data tocontroller 3.

[0025] Controller 3 transforms a shape of lane markers into amathematical model by using a plurality of parameters representative ofa shape of the road shape and a vehicle behavior. By updating theparameters so as to correspond the detection result of the lane markerswith model lane markers, controller 3 detects and recognizes the lanemarkers. On the basis of a present actual yaw rate θ_(REAL) detected bya yaw rate sensor 4 and a vehicle speed V detected by a vehicle speedsensor 5, controller 3 detects a lane keep condition of vehicle VE. Whenvehicle VE is approaching the lane marker and will cross the lanemarker, that is, when vehicle VE tends to deviate the lane, controller 3operates an alarm 6 through an alarm controller 6 a. Alarm 6 gives awarning to a driver by generating warning sound or displaying warninginformation.

[0026] A flowchart of FIG. 3 shows a procedure of a lane markerdetecting process executed by controller 3. The lane marker detectingprocess is a process for detecting lane markers of a road ahead ofvehicle VE and is incorporated by Japanese Patent ProvisionalPublication No. 11-296660 filed by the assignee of the presentinvention.

[0027] At step S1 controller 3 initializes parameters representative ofa road shape and a vehicle behavior (hereinafter, these parameterscalled road parameters). In a X-Y image-plane coordinate system shown inFIG. 4, model lane markers are represented by the following equation (1)using the road parameters.

X=(a+ie)(Y−d)+b/(Y−d)+c  (1)

[0028] where a, b, c, d and e are the road parameters, and i is 1 and 0.Assuming that a vertical dimension between camera 1 and a road surfaceis constant, road parameter a denotes a lateral displacement of vehicleVE between the lane markers, b denotes a road curvature, c denotes a yawangle of vehicle VE (the optical axis of camera 1) relative to the road,d denotes a pitch angle of vehicle VE (the optical axis of camera 1)relative to the road, and e denotes a dimension between the lanemarkers.

[0029] Under the initial condition, the shape of the road and the lanemarkers and the vehicle behavior are set at values corresponding tocenter values, respectively since the shapes of the road and the lanemarkers and the vehicle behavior are not clear in this initialcondition. More specifically, the lateral displacement a of vehicle VEwithin the lane markers is set at a center between the lane markers, theroad curvature b is set at zero (straight), the yaw angle c relative tothe lane markers is set at zero, the pitch angle d relative to the lanemarkers is set at α° indicative of a vehicle stopping condition, and thelane width e between the lane markers is set at a lane width of ahighway representatively defined by the rule of a road structure.

[0030] At step S2 controller 3 initializes small areas for detecting acandidate lane marker. Under the initial condition, since it is supposedthat there is a large difference between the model lane markers obtainedby inputting the initial values into the respective road parameters a toe and the actual lane markers on the image plane, it is preferable thatrelatively large areas are set initially. As shown in FIG. 5, in thisembodiment ten search areas including five right search areas and fiveleft search areas are searched, and the size of each search area is setlarge. If the lane markers have been detected already in the previousprocess, the size of each search area is set small as shown in FIG. 6.The reason thereof is as follows: Since it is assumed that thedifference between the actual lane markers and the model lane markers issmall, a possibility of an erroneous detection of detecting otherobjects will be decreased by setting the size of each search area small.Further this small setting improves the processing speed of thisprocess.

[0031] At step S3 controller 3 receives an image which image processor 2obtains by processing an image taken by camera 1.

[0032] At step S4 controller 3 sets the search areas of the candidatelane markers on the road image received from image processor 2. Duringthis setting, the candidate lane-marker search areas are set so that themodel lane markers are located at centers of the respective search areasas shown in FIG. 7, on the basis of the candidate lane-marker searchareas calculated at step S2 and the model lane markers obtained form theroad parameters corrected at step S1 or S9. As shown in FIG. 7, thenumber of the lane marker search areas is ten constituted by five searchareas for the right lane marker and five search areas for the left lanemarker. It will be understood that the lane marker search areas may beset at positions offset from the model lane markers according to thechange of the past model lane markers.

[0033] At step S5 controller 3 detects the candidate lane marker in eachlane marker search area. In this detecting operation, first adifferential image is produced by filtering the input image with a Sobelfilter. Then controller 3 counts suitable pixels which are located onthe line segment and whose densities are greater than a value capable ofextracting the detection line, with respect to each line segmentgenerated by connecting a point on an upper base line and a point on alower base line of each search area. Further the points on the upper andlower base lines are varied, and as to a predetermined number of theline segments the counting of the suitable pixels are executed. The linesegment, which includes the largest number of the suitable pixels in thewhole line segments, is determined as a detection straight line. Thestart and end of the detection straight line are determined as thecandidate lane marker points. When the number of the suitable pixels ofthe determined detection straight line is smaller than a predeterminedrate to the number of pixels corresponding to the length of the searcharea, controller 3 determines that there is no candidate lane markerpoint in this search area.

[0034] For example, under a condition that the number of pixelscorresponding to the length of the search are is fifteen and thepredetermined rate is ½, if the number of the suitable pixels of thedetection straight line are seven or less, controller 3 determines thatthere is no candidate lane marker point. If the number of the suitablepixels of the detection straight line segment are eight or more,controller 3 determines that the start and the end of the selected linesegment is treated as the candidate line marker points.

[0035] The above operation of determining the candidate lane-markerpoints is executed by each candidate lane-marker search area.

[0036] In determining the candidate lane-marker points, thepredetermined rate may be set at a constant rate throughout all searchareas or may be varied by each search area. Further the predeterminedvalue of the density may be set at a constant value throughout allsearch areas or may be varied by each search area.

[0037] At step S6 controller 3 checks whether the number of thecandidate lane-marker points of the whole candidate lane-marker searcharea is greater than or equal to a predetermined value agreeable todeciding as a lane marker. When the number of the candidate lane markerpoints is smaller than the predetermined value, controller 3 determinesthat there is no lane marker in the search areas, and the routine ofthis flowchart returns to step S2 to again initialize the size of thesearch area. When the number of the candidate lane-marker points isgreater than or equal to the predetermined value, the routine proceedsto step S7.

[0038] At step S7 controller 3 calculates an offset quantity between thedetermined candidate lane-marker point and a point on the model lanemarker obtained by the previous processing by each candidate lane markerpoint.

[0039] At step S8 controller 3 calculates fluctuation quantities Δa, Δb,Δc, Δd and Δe of the road parameters a to e. The calculation of thefluctuation quantities Δa to Δe may be executed on the basis of aleast-square method, for example, disclosed in Japanese PatentProvisional Publication No. 8-5388.

[0040] At step S9 controller 3 corrects road parameters a to e on thebasis of fluctuation quantities Δa to Δe calculated at step S8. When themodel lane marker expressed by the equation (1) is employed, thecorrection of the fluctuation quantities is executed by using thefollowing equations (2). $\begin{matrix}{{a = {a + {\Delta \quad a}}}{b = {b + {\Delta \quad b}}}{c = {c + {\Delta \quad c}}}{d = {d + {\Delta \quad d}}}{e = {e + {\Delta \quad e}}}} & (2)\end{matrix}$

[0041] The corrected road parameters a to e are stored in apredetermined memory area of controller 3 as a road parameters of a newmodel lane markers.

[0042] Following the execution of step S9, the routine returns to stepS3 to repeat the above mentioned routine.

[0043] Controller 3 executes a traveling condition monitoring processfor generating alarm according to the traveling condition of vehicle VE,on the basis of the road parameters of the model lane markers detectedfrom the image information taken by camera 1. That is, the monitoringprocess is executed as shown by a flowchart of FIG. 10.

[0044] At step S11 controller 3 estimates a road shape on the basis ofthe newest road parameters a to e stored in the storage area. Further,controller 3 detects a lateral displacement XL1 at a fixation point A onthe image plane showing a view ahead of vehicle VE. More specifically,as shown in FIG. 11, when the road shape is estimated on the basis ofthe road parameters a to e corrected at step S9, the fixation point A isset at a position (target position) which is ahead of vehicle VE by L1msuch as 30 m and is located at a center between the two model lanemarkers. Therefore, controller 3 detects a distance between the fixationpoint A and the point, which is L1[m] ahead of vehicle VE, as thelateral displacement XL1 relative to the lane center position defined bythe two model lane markers, since camera 1 is set at a laterally centerposition of vehicle VE.

[0045] At step S12 controller 3 reads a vehicle speed V from vehiclespeed sensor 5, and at step S13 controller 3 reads an actual yaw rateθ_(REAL) from yaw rate sensor 4.

[0046] At step S14 controller 3 calculates a target yaw rate θ_(NEED),which is a yaw rate necessary for reaching vehicle VE from the lateraldisplacement position to the lane center, on the basis of lateraldisplacement XL1 at fixation point A and the following equation (3).

θ_(NEED)=(2×XL 1×V)/(L 1×L 1)  (3)

[0047] At step S15 controller 3 calculates a yaw rate difference Δθbetween actual yaw rate θ_(REAL) and target yaw rate θ_(NEED)(Δθ=θ_(REAL)−θ_(NEED)).

[0048] At step S16 controller 3 determines whether an absolute value|Δθ| of yaw rate difference Δθ is greater than a threshold Δ_(TH). Whenthe determination at step S16 is affirmative, that is, when |Δθ|>θ_(TH),the routine proceeds to step S17 wherein controller 3 commands alarmcontroller 6 a to operate alarm 6. By this warning operation, controller3 informs the driver that vehicle VE tends to cross the lane marker.Following the execution of step S18, the routine returns to step S11.When the determination at step S16 is negative, that is, when|Δθ|>θ_(TH), the routine proceeds to step S18 wherein controller 3commands alarm controller 6 a to turn off alarm 6. Following theexecution of step S18, the routine returns to step S11. The thresholdθ_(TH) has previously determined on the basis of experiments. If vehicleVE is traveling while keeping actual yaw rate θ_(REAL) at the thresholdθ_(TH), vehicle VE will deviate from the lane. Camera 1 functions as animage detecting means. Yaw rate sensor 4 functions as an actual turndetecting means. The lane marker detecting process shown in FIG. 3functions as a lane marker detecting means. The road shape estimatingprocess in the lane marker detecting process of FIG. 3 and step S11 ofFIG. 10 functions as a target turn detecting means. Steps S15 to S18 ofFIG. 10 function as lane deviation determining means.

[0049] Next, the manner of operation of the system according to thepresent invention will be discussed.

[0050] When vehicle VE travels on a road, camera 1 takes images ahead ofvehicle VE and sends to image processor 2. Image processor 2 processesthe received images in a predetermined manner of the image processingand sends the processed data (image information) of the image tocontroller 3. Controller 3 executes the lane marker detecting process asto the received image information and updates the road parametersaccording to the road condition at the forward position of vehicle VE.

[0051] Controller 3 estimates the road shape on the basis of thecalculated road parameters and calculates the lateral displacement XL1at the fixation point A on the basis of the estimated road shape asexecuted at step S11 in FIG. 10.

[0052] When vehicle VE travels straight on a center of the lane, camera1 is directed toward the center of the lane and takes images. Therefore,in this vehicle traveling condition, the center of the picture imagetaken by camera 1 generally corresponds to the fixation point A, andthus the lateral displacement XL1 is almost zero. Accordingly, targetyaw rate θ_(NEED) is almost zero. Further, since actual yaw rateθ_(REAL) detected by yaw rate sensor 4 becomes almost zero, the absolutevalue |Δθ| becomes smaller than threshold θ_(TH). Therefore, theprocessing in FIG. 10 moves from step S16 to step S18 wherein controller3 determines that vehicle VE is traveling without deviating from thetraveling lane and therefore the alarm is put in a turned off condition.

[0053] When the road condition to vehicle VE is changed from thestraight road to the right hand curved road shown in FIG. 12, thedirection of camera 1 is offset from the center of the traveling laneand therefore the lateral displacement XL1 becomes large.

[0054] However, since the driver steers vehicle VE so that vehicle VEtravels along the center of the lane, actual yaw rate θ_(REAL) isincreased according to the degree to the steering operation. Therefore,when vehicle VE travels along the center of the lane, actual yaw rateθ_(REAL) generally corresponds to target yaw rate θ_(NEED) calculatedbased on lateral displacement XL1. Due to this correspondence, theabsolute value |Δθ| of the yaw rate difference becomes smaller thanthreshold θ_(TH). Therefore, the processing in FIG. 10 proceeds fromstep S16 and to step S18 wherein the alarm is put in a turned offcondition.

[0055] When vehicle VE is turning along the center of the lane, actualyaw rate θ_(REAL) generally corresponds to target yaw rate θ_(NEED)calculated based on lateral displacement XL1. Therefore, in this turningcondition, the alarm is put in a turned off condition.

[0056] Further when vehicle VE tends to deviate from the lane from theturning condition along the center of the lane, actual yaw rate θ_(REAL)cannot satisfy target yaw rate θ_(NEED), and therefore the absolutevalue |Δθ| of the yaw rate difference Δθ becomes large. Further, whenthe absolute value |Δθ| becomes larger than threshold θ_(TH), controller3 determines that there is a possibility that vehicle VE deviates fromthe traveling lane. Accordingly, the processing in FIG. 10 proceeds fromstep S16 to step S17 to generate warning sound or warning information.In reply to this warning information, the driver executes the steeringoperation, and therefore vehicle VE can keep traveling on the lanewithout deviating from the lane.

[0057] On the other hand, when vehicle VE enters a curved withoutexecuting a steering operation of traveling vehicle VE along the curve,vehicle VE is not traveling along the lane. Therefore, the direction ofcamera 1 is changed, and the center of the picture image is offset fromthe center of the lane. Consequently, the lateral displacement XL1gradually increases. Although target yaw rate θ_(NEED) also increases,actual yaw rate θ_(REAL) detected by yaw rate sensor 4 does not increaseand generally keeps constant. Accordingly, yaw rate difference Δθbetween target yaw rate and actual yaw rate gradually increases, andwhen the absolute value |Δθ| of the difference becomes larger thanthreshold θ_(TH), alarm 6 generates warning information.

[0058] With the thus arranged system according to the present invention,when target yaw rate θ_(NEED) necessary for traveling vehicle VEspecified by the lateral displacement XL1 along the center of the laneis compared with actual yaw rate θ_(REAL) and when the differencetherebetween is large, that is, when the curved condition of the roadahead of vehicle VE is compared with the turn condition of vehicle VEand when they do not match with each other, the system generates warninginformation. Accordingly, it is possible to generate warning informationonly at the time when the yaw rate is suddenly changed such as in thecase of entering the corner of the traveling road. Further, it ispossible to accurately generate warning information without erroneouslygenerating warning information as in the case that the lane deviation isdetected on the basis of a relative distance between vehicle VE and lanemarkers.

[0059] Furthermore, such an accurate warning effectively assists thetraveling of vehicle VE. Additionally, since the system according to thepresent invention is arranged to determine based on actual yaw rateθ_(REAL) whether vehicle VE deviates from a lane, it becomes possible todetect deviating from the lane before vehicle VE actually deviates fromthe lane.

[0060] Next, referring to FIGS. 13 and 14, there is shown a secondembodiment of the lane-keep assisting system according to the presentinvention. The second embodiment is basically the same as the firstembodiment except for a setting method of threshold θ_(TH). Accordingly,the same parts are denoted by the same reference numerals and theexplanation thereof is omitted herein.

[0061] As shown in FIG. 13, the traveling condition monitoring processof the second embodiment further includes step S15 a in addition tosteps S11 to S18 shown in FIG. 10 of the first embodiment.

[0062] At step S15 a following the execution of step S15, controller 3sets threshold θ_(TH) according to vehicle speed V. More specifically, athreshold map representative of a relationship between threshold θ_(TH)and vehicle speed V has previously stored in memory area of controller3. Controller 3 determines threshold θ_(TH) on the basis of vehiclespeed V read at step S12 and the threshold map. The threshold map is setsuch that threshold θ_(TH) decreases as vehicle speed V increases. Thatis, since a time period for reaching the lane deviation is shortenedaccording to the increase of vehicle speed V, it is necessary to detectthe lane deviating condition earlier according to the increase ofvehicle speed V. By employing the threshold map, the alarm timing isprompted according to the increase of the vehicle speed.

[0063] When the absolute value |Δθ| calculated at step S15 is greaterthan threshold θ_(TH) determined at step S15 a, the routine proceedsfrom step S16 to step S17 wherein alarm 6 generates alarm information.Since the second embodiment is arranged to set threshold θ_(TH)according to vehicle speed V, it is possible to detect a lane-deviatingcondition at an earlier time as vehicle speed V increases. This earlierdetection according to vehicle speed enables generates warninginformation before vehicle deviates from the lane regardless vehiclespeed V, and such an accurate warning effectively assists the travelingof vehicle VE. It is of course that the second embodiment ensures theadvantages derived by the first embodiment.

[0064] Next, referring to FIGS. 15 and 16, there will be discussed athird embodiment of the lane-keep assisting system according to thepresent invention. As shown in FIG. 15, the third embodiment isbasically the same as the first embodiment except that there is furtherprovided brake actuators 16 for generating braking force to wheels and abrake controller 16 a for operating brake actuators 16 according to acommand from controller 3, in addition to the arrangement of the firstembodiment shown in FIG. 1. The same parts are denoted by the samereference numerals and the explanation thereof is omitted herein.

[0065] As shown in FIG. 16, the traveling condition monitoring processof the third embodiment employs steps S19 and S20 instead of steps S17and S18, as compared with the flowchart of FIG. 13 of the secondembodiment.

[0066] When controller 3 determines at step S16 that the absolute value|Δθ| is greater than threshold θ_(TH) (|Δθ|>θ_(TH)), the routineproceeds from step S16 to step S19 wherein controller 3 commands alarmcontroller 6 a to operate alarm 6 so as to generate alarm informationand commands brake controller 16 a to operate brake actuators 16 so asto generate braking force for avoiding vehicle VE from deviating fromthe lane. After the braking force is applied to the wheels by operatingbrake actuators 16, the routine returns to step S11.

[0067] On the other hand, when controller 3 determines at step S16 that|Δθ|≦θ_(TH), the routine proceeds to step S20 wherein controller 3commands alarm controller 6 a to turn off alarm 6 and commands brakecontroller 16 a to put brake actuators 16 into an inoperative conditionso as to stop generating the braking force for avoiding vehicle VE fromdeviating from the lane. Thereafter, the routine returns to step S11.Steps S19 and S20 functions as a braking means and a braking controlmeans.

[0068] Accordingly, when it is determined that there is a possibilitythat vehicle VE deviates from the lane, the warning information isgenerated by alarm 6 and braking force is generated by brake actuators16. These operations suppress the degree of the lane deviation andelongates the time reaching the deviation of the lane.

[0069] Although the third embodiment has been shown and described suchthat both of alarm 6 and brake actuators 16 are operated according tothe lane deviation determination, it will be understood that theinvention is not limited to this and may be arranged to operate onlybrake actuators 16. Further, although the third embodiment has beenshown and described such that when controller 3 executes a processingfor decreasing vehicle speed V by operating brake actuators 16 whencontroller determines that vehicle VE tends to deviate from the lane byoperating brake actuators 16, it will be understood that the inventionis not limited to this and may employ the other vehicle speed decreasingmeans. For example, the system according to the present invention may bearranged such that an output of an engine or motor of vehicle VE isdecreased or a shift-down operation of a transmission is executed whencontroller 3 determines that vehicle VE tends to deviate from the lane.

[0070] While the embodiments according to the present invention havebeen shown and described such that yaw rate sensor 4 is employed as aturn condition detecting means, it will be understood that a steeringangle sensor may be employed instead of yaw rate sensor 4 and an actualyaw rate may be estimated on the basis of the steering angle detectingby the steering-angle sensor and vehicle speed V detected by vehiclespeed sensor 5.

[0071] Further, a lateral acceleration may be employed instead of yawrate. In such lateral acceleration employed case, a target lateralacceleration Y_(G-NEED), by which vehicle VE moves from a position apartfrom the forward fixation point by lateral displacement XL1 to thecenter of the lane, is calculated from the following equation (4).

Y _(G-NEED)=(2×XL 1×V×V)/(L 1×L 1)  (4)

[0072] A lateral acceleration sensor is employed instead of yaw ratesensor 4.

[0073] When an absolute value of a difference between the actual lateralacceleration detected by the lateral acceleration sensor and targetlateral acceleration Y_(G-NEED) calculated from the equation (4) becomesgreater than a preset threshold Y_(G-TH), controller 3 determines thatthere is a possibility that vehicle VE deviates from the lane, andcommands alarm controller 6 a to operate alarm 6. Accordingly, ifvehicle VE is traveling while keeping the lateral acceleration greaterthan or equal to the threshold Y_(G-TH), it is forecasted that vehicleVE deviates from the lane.

[0074] The threshold Y_(G-TH) is varied according to vehicle speed V soas to be decreased according to the increase of vehicle speed V.Accordingly, by this variation of threshold Y_(G-TH) according tovehicle speed V, it becomes possible to firmly generate warninginformation at a time before vehicle VE deviates from the lane, even ifvehicle VE travels at a high vehicle speed. Further, a steering anglesensor may be employed instead of the lateral acceleration sensor, andan actual yaw rate may be estimated on the basis of the steering angledetecting by the steering angle sensor and vehicle speed V detected byvehicle speed sensor 5.

[0075] Although the embodiments according to the present invention havebeen shown and described such that the fixation point A is set at thecenter portion between the model lane markers corresponding to thecenter of the lane and the requested yaw rate for reaching vehicle VE tothe fixation point A, it will be understood that the invention is notlimited to this arrangement, and the fixation point may be set at theother position such as a position where vehicle VE can travels along thelane without deviated from the lane.

[0076] Further, although the embodiments according to the presentinvention have been shown and described such that the lane markers aredetected by executing the image processing as to picture images taken bycamera 1 and that the road shape is estimated on the basis of thedetected lane markers, it will be understood that the invention is notlimited to this arrangement and the other road shape detecting means fordetecting a road shape ahead of vehicle VE may be employed.

[0077] This application is based on a prior Japanese Patent ApplicationNo. 2000-269562 filed on Sep. 6, 2000 in Japan. The entire contents ofthis Japanese Patent Application are hereby incorporated by reference.

[0078] Although the invention has been described above by reference to acertain embodiment of the invention, the invention is not limited to theembodiments described above. Modifications and variations of theembodiment described above will occur to those skilled in the art, inlight of the above teaching. The scope of the invention is defined withreference to the following claims.

What is claimed is:
 1. A system for assisting a lane-keep traveling of avehicle, comprising: a road image detector taking a view ahead of thevehicle; a vehicle behavior detector detecting a behavior of thevehicle; and a controller coupled to the road image sensor and thevehicle behavior detector, the controller being arranged, to calculate aroad shape on the basis of the view taken by the road image detector, tocalculate a target turn indicative value indicative of a target turn forreaching the vehicle to a target position, on the basis of the roadshape detected, to calculate an actual turn indicative value indicativeof an actual turn of the vehicle, and to determine whether the vehicleapproaches a lane boundary of a traveling lane, on the basis of thetarget turn indicative value and the actual turn indicative value. 2.The system as claimed in claim 1, wherein the controller determines thatthe vehicle approaches the lane boundary when a difference between thetarget turn indicative value and the actual turn indicative value isgreater than a threshold.
 3. The system as claimed in claim 1, whereinthe road image detector includes a camera that takes a picture imageshowing a view ahead of the vehicle, and an image processor thatprocesses the picture image in order to detect lane markerscorresponding to the lane boundaries of the traveling lane.
 4. Thesystem as claimed in claim 3, wherein the controller determines thetarget turn indicative value on the basis of an offset quantity betweena direction of the target position and a direction of the cameradirected ahead of the vehicle.
 5. The system as claimed in claim 2,wherein the vehicle behavior detector includes a vehicle speed detectorthat detects a speed of the vehicle, and the threshold is decreased asthe speed of the vehicle is increased.
 6. The system as claimed in claim1, wherein the target turn indicative value includes a target yaw rate,and the actual turn indicative value includes an actual yaw rategenerated at the vehicle.
 7. The system as claimed in claim 6, whereinthe actual yaw rate is estimated from a steering angle and a speed ofthe vehicle.
 8. The system as claimed in claim 1, wherein the targetturn indicative value includes a target lateral acceleration, and theactual turn indicative value includes an actual lateral accelerationgenerated at the vehicle.
 9. The system as claimed in claim 8, whereinthe actual lateral acceleration is estimated from a steering angle and aspeed of the vehicle.
 10. The system as claimed in claim 1, furthercomprising an alarm that generate alarm information and an alarmcontroller that controls an operation of the alarm, wherein the alarmcontroller operates the alarm to generate alarm when the controllerdetermines that the vehicle approaches the lane boundary.
 11. The systemas claimed in claim 1, further comprising a brake actuator thatgenerates a braking force and a brake controller that controls anoperation of the brake actuator, wherein the brake controller operatesthe brake actuator to generate the braking force when the controllerdetermines that the vehicle approaches the lane boundary.
 12. The systemas claimed in claim 1, further comprising a driving-force generator thatgenerates a driving force of the vehicle and a driving-force controllerthat controls an operation of the driving-force generator, wherein thedriving-force controller controls the driving-force generator todecrease the driving force when the vehicle is approaching the laneboundary.
 13. The system as claimed in claim 1, wherein the targetposition includes a center position between the lane boundaries ahead ofthe vehicle.
 14. A lane deviation determining system of a vehiclecomprising: road shape detecting means for detecting a shape of a roadahead of the vehicle; target turn detecting means for detecting a valueindicative of a target turn necessary for reaching the vehicle to atarget position on the basis of the road shape detected; actual turndetecting means for detecting a value indicative of an actual turn ofthe vehicle; and lane deviation determining means for determining thatthe vehicle tends to deviate from a traveling lane on the basis of thetarget turn indicative value and the actual turn indicative value.
 15. Amethod for assisting a lane keep traveling of a vehicle, the methodcomprising: taking a view ahead of the vehicle; detecting a behavior ofthe vehicle; calculating a road shape on the basis of the view;calculating a target turn indicative value indicative of a target turnfor reaching the vehicle to a target position, on the basis of the roadshape calculated; calculating an actual turn indicative value indicativeof an actual turn of the vehicle on the basis of the behavior of thevehicle; and determining whether the vehicle approaches a lane boundaryof a traveling lane, on the basis of the target turn indicative valueand the actual turn indicative value.